For years, Calais' port infrastructure has been running at full capacity, creating an urgent need to expand seaward. Following consultation in 2015, the Nord Pas de Calais Regional Council awarded the contract to expand the port to a consortium of specialists.

Background

The Port of Calais is France's busiest port for passenger traffic and the fourth busiest in Europe. Every year, around 10 million passengers pass through the port on more than 18,000 journeys. On average, a ship departs every 30 minutes.Worth 675 million euros, the two-phase project to expand the port consists of an access channel for large vessels, a 3.2 km breakwater and a turning basin.

The company responsible for the groundwork phase of the project, Jan De Nul Group, reclaimed the land for the expansion by dredging 4 million m3 of sand. This will make way for 65 ha of additional land and house three extra ferry terminals.

Based in Luxembourg, Jan De Nul Group is the world's largest dredging company. It has a fleet of over 75 vessels and previously expanded the Panama Canal and created Palm Island in Dubai. In Calais, Jan De Nul Group carried out the land reclamation and constructed a 3.2 km breakwater, a coastal structure used to create an enclosed harbour protected from the rough weather. To follow the progress of the rock installation, the company needed a way to take topographical measurements of the expansion quickly, reliably and safely.

Merlin is perfect for our measurement needs, producing high-quality, reliable data despite the demanding marine environment. New users find it easy to operate and, during initial trials, Merlin easily handled wave heights of 1.5 m and speeds of 6 kt at a distance of 75 m from the breakwater, producing a high-resolution scan of the accropodes and other complex vertical structures. Merlin easily calibrates with our existing sensor hardware and on-board software, outperforming other conventional and photogrammetric measurement tools.

Jan De Nul Group (Luxembourg)

Challenge

Marine environments are usually surveyed by taking two types of measurement: bathymetric and topographical. The first measures the size and depth of the subsea relief below the waterline and the second measures the coastal terrain and placement of structures above the waterline.

“Surveying the underwater terrain has never been a problem because we use multibeam sonar technology mounted onto a survey vessel,” explains Mike Lycke, Jan De Nul Group's Project Survey Manager at the Calais site. “However, the part above the water has always been difficult to survey. The breakwater is made up of layers of rock, starting with small ones on the seabed, rising to rocks weighing up to 4 tonnes at the top of the breakwater.

“To further reinforce the structure, the outer perimeter of the breakwater is lined with X-blocks, large interlocking concrete blocks that measure up to 14 m3, weigh around 30 tonnes each and dissipate the energy from the crashing waves.

“Because the breakwater only becomes stable when all the layers are installed, any delays in the construction mean that bad weather and tidal forces can erode the structure and it has to be rebuilt, which slows down the project and has a knock-on effect on the progress of the breakwater construction as the eroded slopes need to be repaired. Therefore, it is important that we regularly survey for an accurate as-built dossier of the breakwater and to guarantee the breakwater is built according to the required specification.

“Traditionally, carrying out a topographical survey was a dangerous manual process. It involved a person climbing onto the slippery rocks with a total station and taking measurements by hand. The only protection was a life jacket, and the process could take up to 12 hours. Even then, the survey data was crude and resulted in slow progress.

“We subsequently trialled a vehicle-mounted laser scanner on a survey vessel and experienced many problems with it. Not only was it difficult to fit – calibrating the system with the multibeam sensors was a challenge – its built-in inertial navigation system, which was primarily designed for land applications, struggled to compensate for the vessel's motion on water. Finally, the date time-stamping data produced by that unit did not align with the vessel's on-board GNSS satellite navigation system, calling the data into question.”

Solution

In its search for the ideal survey system, Jan De Nul Group turned to its supplier network and found Renishaw through the company's local reseller AllTerra Belux. Having identified Jan De Nul Group's surveying needs, Renishaw delivered Merlin, a vessel-based lidar system capable of producing a detailed 3D scan of the breakwater.

“We've engineered Merlin to seamlessly integrate with a survey vessel's below-water sensors,” explains John Howells, Marine Sales Manager at Renishaw. “Merlin's time-tagged data synchronises with the sonar equipment to capture a homogeneous dataset above and below the water line, eliminating the need for the survey vessel to make two trips.

“The unit is robustly secured on the vessel using a flange plate. This ensures Merlin remains in the same position regardless of any variation in the pitch or heading of the vessel. It also means that the user can switch Merlin from one vessel to another, easily adjust mounting angles and quickly calibrate patch-test values to perfectly align with the sonar sensors.”

Crucially, Merlin integrates with any existing marine-grade motion sensor and is compatible with a variety of on-board navigation and data acquisition software such as QPS's QINSy. A single cable carries both power and data between Merlin and the Renishaw interface box, which connects to an on-board computer via Ethernet. The acquisition software uses the laser data generated by Merlin to create a geo-referenced 3D model or ‘point cloud' of the surrounding environment.

Results

Before introducing Merlin, a typical survey could take up to 12 hours and involve surveyors climbing onto slippery rocks in potentially hazardous conditions. Using Merlin, it now takes just 15 minutes and does not require personnel to take unnecessary risks with their safety.

“Renishaw's Merlin has given us a lot of flexibility in mapping the precise placement of accropodes on the breakwater as well as the wider topographical features of the expansion project at the port,” enthuses David Claeys, Area Survey Manager at Jan De Nul Group. “The tide at the Calais site varies by up to 7 m each day, but Merlin is capable of operating at varying wave heights, speeds and distances from the coastal features.

“We can also now stream the data Merlin generates, directly from the vessel to our offices at the port in real-time. The man-hours saved with Merlin not only deliver significant cost savings but also allow the engineers working on the project to make more informed decisions, more quickly.”

Impressed with the results at Calais, Jan De Nul Group is now looking at fitting a survey vessel with two units, one on the port side and one on the starboard side, which will have the effect of increasing the field of view and improving the point cloud coverage.

With operations around the world, Jan De Nul Group continues to deliver major marine engineering works in regions as far flung as Hong Kong and Qatar. The ease with which Merlin can be moved from one vessel to another means that having delivered success in Calais, the Merlin unit can be deployed quickly on other projects around the world.

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For years, Calais’ port infrastructure has been running at full capacity, creating an urgent need to expand seaward. Following consultation in 2015, the Nord Pas de Calais Regional Council awarded the contract to expand the port to a consortium of specialists.

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